His implication was that a -3 DRS for a UTIL player at one position wasn't a problem at all. He was there as a backup or injury insurance. He said you can live with that deficiency because the player is able to move around the field. Again, if he's a plus at 2B/3B (maybe) then you can ignore him being a slight minus at SS. He's not saying that defense is good at all, just that you can live with it.
You said "it's really bad" which I disagree with for sure. Small sample sized DRS doesn't extrapolate well over 162 games. For example, Rafaela had a -4 DRS due to one or two plays early on. Was that indicative of his defense? Probably not! He's already at a 1 DRS a few weeks later. If DHam played SS fulltime, the additional reps could get him more comfortable to fielding the position such that his -3 may only be a -4 for the full season. That's Xander Bogaerts-esque. Better than Story or Bichette were last season.